This invention relates to a proximity switch and, more particularly, to a proximity switch with two connecting wires for switching an alternating current.
One of the known proximity switches has two connecting wires to be connected in series to a load and to a power source, which is a so-called two wire self-contained proximity switch. Power lines and output lines in such proximity switch are in common, so that it needs only two connecting wires and its switch action is similar to that of a limit switch. It is desirable that both the residual voltage under "ON" condition and the residual current under "OFF" condition are zero as in a limit switch.
A constant d.c. power supply, converted from an a.c. power source, to a detecting circuit, however, is required regardless of "ON" or "OFF" condition.
For this purpose, a certain value of residual voltage and of residual current must be retained. So it is very important in such proximity switch to minimize the residual voltage and residual current.
A proximity switch provided with an operation indicator is useful. A known proximity switch has an operation indicator consisting in a light-emitting diode. Such indicator, however, is preferably interposed in an electric circuit of the proximity switch not to increase the residual voltage or residual current. Further, it is desirable that the indicator of a normal-close type proximity switch operate only when an object is detected in the vicinity of a detecting means.
It is an object of this invention to provide a proximity switch of which residual voltage is low.
It is another object of this invention to provide a proximity switch of which residual current is low.
It is a further object of this invention to provide a proximity switch provided with an operation indicator which operates without an increase of residual voltage or residual current.
It is a still further object of this invention to provide a normal-close type proximity switch provided with an operation indicator which operates upon detection of an object in the vicinity of a detection means.
It should be understood that the term "proximity switch" is used herein to refer to any and all contactless switches which detect an object in the vicinity of its detection means such as a coil, capacitor or photodiode.